//     Backbone.js 0.5.3
//     (c) 2010 Jeremy Ashkenas, DocumentCloud Inc.
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://documentcloud.github.com/backbone


(function (root, factory) {
    // Set up Backbone appropriately for the environment.
    if (typeof exports !== 'undefined') {
        // Node/CommonJS, no need for jQuery in that case.
        factory(root, exports, require('underscore'));
    } else if (typeof define === 'function' && define.amd) {
        // AMD
        define('backbone', ['underscore', 'jquery', 'exports'], function (_, $, exports) {
            factory(root, exports, _, $);
        });
    } else {
        // Browser globals
        root.Backbone = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender));
    }
} (this, function (root, Backbone, _, $) {

    // Initial Setup
    // -------------

    // Save the previous value of the `Backbone` variable.
    var previousBackbone = root.Backbone;

    // Create a local reference to slice.
    var slice = Array.prototype.slice;

    // Current version of the library. Keep in sync with `package.json`.
    Backbone.VERSION = '0.5.3';

    // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
    // to its previous owner. Returns a reference to this Backbone object.
    Backbone.noConflict = function () {
        root.Backbone = previousBackbone;
        return Backbone;
    };

    // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option will
    // fake `"PUT"` and `"DELETE"` requests via the `_method` parameter and set a
    // `X-Http-Method-Override` header.
    Backbone.emulateHTTP = false;

    // Turn on `emulateJSON` to support legacy servers that can't deal with direct
    // `application/json` requests ... will encode the body as
    // `application/x-www-form-urlencoded` instead and will send the model in a
    // form param named `model`.
    Backbone.emulateJSON = false;

    // Backbone.Events
    // -----------------

    // A module that can be mixed in to *any object* in order to provide it with
    // custom events. You may `bind` or `unbind` a callback function to an event;
    // `trigger`-ing an event fires all callbacks in succession.
    //
    //     var object = {};
    //     _.extend(object, Backbone.Events);
    //     object.bind('expand', function(){ alert('expanded'); });
    //     object.trigger('expand');
    //
    Backbone.Events = {

        // Bind an event, specified by a string name, `ev`, to a `callback` function.
        // Passing `"all"` will bind the callback to all events fired.
        bind: function (ev, callback, context) {
            var calls = this._callbacks || (this._callbacks = {});
            var list = calls[ev] || (calls[ev] = {});
            var tail = list.tail || (list.tail = list.next = {});
            tail.callback = callback;
            tail.context = context;
            list.tail = tail.next = {};
            return this;
        },

        // Remove one or many callbacks. If `callback` is null, removes all
        // callbacks for the event. If `ev` is null, removes all bound callbacks
        // for all events.
        unbind: function (ev, callback) {
            var calls, node, prev;
            if (!ev) {
                this._callbacks = {};
            } else if (calls = this._callbacks) {
                if (!callback) {
                    calls[ev] = {};
                } else if (node = calls[ev]) {
                    while ((prev = node) && (node = node.next)) {
                        if (node.callback !== callback) continue;
                        prev.next = node.next;
                        node.context = node.callback = null;
                        break;
                    }
                }
            }
            return this;
        },

        // Trigger an event, firing all bound callbacks. Callbacks are passed the
        // same arguments as `trigger` is, apart from the event name.
        // Listening for `"all"` passes the true event name as the first argument.
        trigger: function (eventName) {
            var node, calls, callback, args, ev, events = ['all', eventName];
            if (!(calls = this._callbacks)) return this;
            while (ev = events.pop()) {
                if (!(node = calls[ev])) continue;
                args = ev == 'all' ? arguments : slice.call(arguments, 1);
                while (node = node.next) if (callback = node.callback) callback.apply(node.context || this, args);
            }
            return this;
        }

    };

    // Backbone.Model
    // --------------

    // Create a new model, with defined attributes. A client id (`cid`)
    // is automatically generated and assigned for you.
    Backbone.Model = function (attributes, options) {
        var defaults;
        attributes || (attributes = {});
        if (defaults = this.defaults) {
            if (_.isFunction(defaults)) defaults = defaults.call(this);
            attributes = _.extend({}, defaults, attributes);
        }
        this.attributes = {};
        this._escapedAttributes = {};
        this.cid = _.uniqueId('c');
        this.set(attributes, { silent: true });
        this._changed = false;
        this._previousAttributes = _.clone(this.attributes);
        if (options && options.collection) this.collection = options.collection;
        this.initialize(attributes, options);
    };

    // Attach all inheritable methods to the Model prototype.
    _.extend(Backbone.Model.prototype, Backbone.Events, {

        // Has the item been changed since the last `"change"` event?
        _changed: false,

        // The default name for the JSON `id` attribute is `"id"`. MongoDB and
        // CouchDB users may want to set this to `"_id"`.
        idAttribute: 'id',

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function () { },

        // Return a copy of the model's `attributes` object.
        toJSON: function () {
            return _.clone(this.attributes);
        },

        // Get the value of an attribute.
        get: function (attr) {
            return this.attributes[attr];
        },

        // Get the HTML-escaped value of an attribute.
        escape: function (attr) {
            var html;
            if (html = this._escapedAttributes[attr]) return html;
            var val = this.attributes[attr];
            return this._escapedAttributes[attr] = _.escape(val == null ? '' : '' + val);
        },

        // Returns `true` if the attribute contains a value that is not null
        // or undefined.
        has: function (attr) {
            return this.attributes[attr] != null;
        },

        // Set a hash of model attributes on the object, firing `"change"` unless you
        // choose to silence it.
        set: function (attrs, options) {

            // Extract attributes and options.
            options || (options = {});
            if (!attrs) return this;
            if (attrs.attributes) attrs = attrs.attributes;
            var now = this.attributes, escaped = this._escapedAttributes;

            // Run validation.
            if (!options.silent && this.validate && !this._performValidation(attrs, options)) return false;

            // Check for changes of `id`.
            if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];

            // We're about to start triggering change events.
            var alreadyChanging = this._changing;
            this._changing = true;

            // Update attributes.
            for (var attr in attrs) {
                var val = attrs[attr];
                if (!_.isEqual(now[attr], val)) {
                    now[attr] = val;
                    delete escaped[attr];
                    this._changed = true;
                    if (!options.silent) this.trigger('change:' + attr, this, val, options);
                }
            }

            // Fire the `"change"` event, if the model has been changed.
            if (!alreadyChanging && !options.silent && this._changed) this.change(options);
            this._changing = false;
            return this;
        },

        // Remove an attribute from the model, firing `"change"` unless you choose
        // to silence it. `unset` is a noop if the attribute doesn't exist.
        unset: function (attr, options) {
            if (!(attr in this.attributes)) return this;
            options || (options = {});
            var value = this.attributes[attr];

            // Run validation.
            var validObj = {};
            validObj[attr] = void 0;
            if (!options.silent && this.validate && !this._performValidation(validObj, options)) return false;

            // changedAttributes needs to know if an attribute has been unset.
            (this._unsetAttributes || (this._unsetAttributes = [])).push(attr);

            // Remove the attribute.
            delete this.attributes[attr];
            delete this._escapedAttributes[attr];
            if (attr == this.idAttribute) delete this.id;
            this._changed = true;
            if (!options.silent) {
                this.trigger('change:' + attr, this, void 0, options);
                this.change(options);
            }
            return this;
        },

        // Clear all attributes on the model, firing `"change"` unless you choose
        // to silence it.
        clear: function (options) {
            options || (options = {});
            var attr;
            var old = this.attributes;

            // Run validation.
            var validObj = {};
            for (attr in old) validObj[attr] = void 0;
            if (!options.silent && this.validate && !this._performValidation(validObj, options)) return false;

            this.attributes = {};
            this._escapedAttributes = {};
            this._changed = true;
            if (!options.silent) {
                for (attr in old) {
                    this.trigger('change:' + attr, this, void 0, options);
                }
                this.change(options);
            }
            return this;
        },

        // Fetch the model from the server. If the server's representation of the
        // model differs from its current attributes, they will be overriden,
        // triggering a `"change"` event.
        fetch: function (options) {
            options || (options = {});
            var model = this;
            var success = options.success;
            options.success = function (resp, status, xhr) {
                if (!model.set(model.parse(resp, xhr), options)) return false;
                if (success) success(model, resp);
            };
            options.error = wrapError(options.error, model, options);
            return (this.sync || Backbone.sync).call(this, 'read', this, options);
        },

        // Set a hash of model attributes, and sync the model to the server.
        // If the server returns an attributes hash that differs, the model's
        // state will be `set` again.
        save: function (attrs, options) {
            options || (options = {});
            if (attrs && !this.set(attrs, options)) return false;
            var model = this;
            var success = options.success;
            options.success = function (resp, status, xhr) {
                if (!model.set(model.parse(resp, xhr), options)) return false;
                if (success) success(model, resp, xhr);
            };
            options.error = wrapError(options.error, model, options);
            var method = this.isNew() ? 'create' : 'update';
            return (this.sync || Backbone.sync).call(this, method, this, options);
        },

        // Destroy this model on the server if it was already persisted. Upon success, the model is removed
        // from its collection, if it has one.
        destroy: function (options) {
            options || (options = {});
            if (this.isNew()) return this.trigger('destroy', this, this.collection, options);
            var model = this;
            var success = options.success;
            options.success = function (resp) {
                model.trigger('destroy', model, model.collection, options);
                if (success) success(model, resp);
            };
            options.error = wrapError(options.error, model, options);
            return (this.sync || Backbone.sync).call(this, 'delete', this, options);
        },

        // Default URL for the model's representation on the server -- if you're
        // using Backbone's restful methods, override this to change the endpoint
        // that will be called.
        url: function () {
            var base = getUrl(this.collection) || this.urlRoot || urlError();
            if (this.isNew()) return base;
            return base + (base.charAt(base.length - 1) == '/' ? '' : '/') + encodeURIComponent(this.id);
        },

        // **parse** converts a response into the hash of attributes to be `set` on
        // the model. The default implementation is just to pass the response along.
        parse: function (resp, xhr) {
            return resp;
        },

        // Create a new model with identical attributes to this one.
        clone: function () {
            return new this.constructor(this);
        },

        // A model is new if it has never been saved to the server, and lacks an id.
        isNew: function () {
            return this.id == null;
        },

        // Call this method to manually fire a `change` event for this model.
        // Calling this will cause all objects observing the model to update.
        change: function (options) {
            this.trigger('change', this, options);
            this._previousAttributes = _.clone(this.attributes);
            this._unsetAttributes = null;
            this._changed = false;
        },

        // Determine if the model has changed since the last `"change"` event.
        // If you specify an attribute name, determine if that attribute has changed.
        hasChanged: function (attr) {
            if (attr) return this._previousAttributes[attr] != this.attributes[attr];
            return this._changed;
        },

        // Return an object containing all the attributes that have changed, or false
        // if there are no changed attributes. Useful for determining what parts of a
        // view need to be updated and/or what attributes need to be persisted to
        // the server. Unset attributes will be set to undefined.
        changedAttributes: function (now) {
            now || (now = this.attributes);
            var old = this._previousAttributes, unset = this._unsetAttributes;

            var changed = false;
            for (var attr in now) {
                if (!_.isEqual(old[attr], now[attr])) {
                    changed || (changed = {});
                    changed[attr] = now[attr];
                }
            }

            if (unset) {
                changed || (changed = {});
                var len = unset.length;
                while (len--) changed[unset[len]] = void 0;
            }

            return changed;
        },

        // Get the previous value of an attribute, recorded at the time the last
        // `"change"` event was fired.
        previous: function (attr) {
            if (!attr || !this._previousAttributes) return null;
            return this._previousAttributes[attr];
        },

        // Get all of the attributes of the model at the time of the previous
        // `"change"` event.
        previousAttributes: function () {
            return _.clone(this._previousAttributes);
        },

        // Run validation against a set of incoming attributes, returning `true`
        // if all is well. If a specific `error` callback has been passed,
        // call that instead of firing the general `"error"` event.
        _performValidation: function (attrs, options) {
            var error = this.validate(attrs);
            if (error) {
                if (options.error) {
                    options.error(this, error, options);
                } else {
                    this.trigger('error', this, error, options);
                }
                return false;
            }
            return true;
        }

    });

    // Backbone.Collection
    // -------------------

    // Provides a standard collection class for our sets of models, ordered
    // or unordered. If a `comparator` is specified, the Collection will maintain
    // its models in sort order, as they're added and removed.
    Backbone.Collection = function (models, options) {
        options || (options = {});
        if (options.comparator) this.comparator = options.comparator;
        _.bindAll(this, '_onModelEvent', '_removeReference');
        this._reset();
        if (models) this.reset(models, { silent: true });
        this.initialize.apply(this, arguments);
    };

    // Define the Collection's inheritable methods.
    _.extend(Backbone.Collection.prototype, Backbone.Events, {

        // The default model for a collection is just a **Backbone.Model**.
        // This should be overridden in most cases.
        model: Backbone.Model,

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function () { },

        // The JSON representation of a Collection is an array of the
        // models' attributes.
        toJSON: function () {
            return this.map(function (model) { return model.toJSON(); });
        },

        // Add a model, or list of models to the set. Pass **silent** to avoid
        // firing the `added` event for every new model.
        add: function (models, options) {
            if (_.isArray(models)) {
                for (var i = 0, l = models.length; i < l; i++) {
                    this._add(models[i], options);
                }
            } else {
                this._add(models, options);
            }
            return this;
        },

        // Remove a model, or a list of models from the set. Pass silent to avoid
        // firing the `removed` event for every model removed.
        remove: function (models, options) {
            if (_.isArray(models)) {
                for (var i = 0, l = models.length; i < l; i++) {
                    this._remove(models[i], options);
                }
            } else {
                this._remove(models, options);
            }
            return this;
        },

        // Get a model from the set by id.
        get: function (id) {
            if (id == null) return null;
            return this._byId[id.id != null ? id.id : id];
        },

        // Get a model from the set by client id.
        getByCid: function (cid) {
            return cid && this._byCid[cid.cid || cid];
        },

        // Get the model at the given index.
        at: function (index) {
            return this.models[index];
        },

        // Force the collection to re-sort itself. You don't need to call this under normal
        // circumstances, as the set will maintain sort order as each item is added.
        sort: function (options) {
            options || (options = {});
            if (!this.comparator) throw new Error('Cannot sort a set without a comparator');
            this.models = this.sortBy(this.comparator);
            if (!options.silent) this.trigger('reset', this, options);
            return this;
        },

        // Pluck an attribute from each model in the collection.
        pluck: function (attr) {
            return _.map(this.models, function (model) { return model.get(attr); });
        },

        // When you have more items than you want to add or remove individually,
        // you can reset the entire set with a new list of models, without firing
        // any `added` or `removed` events. Fires `reset` when finished.
        reset: function (models, options) {
            models || (models = []);
            options || (options = {});
            this.each(this._removeReference);
            this._reset();
            this.add(models, { silent: true });
            if (!options.silent) this.trigger('reset', this, options);
            return this;
        },

        // Fetch the default set of models for this collection, resetting the
        // collection when they arrive. If `add: true` is passed, appends the
        // models to the collection instead of resetting.
        fetch: function (options) {
            options || (options = {});
            var collection = this;
            var success = options.success;
            options.success = function (resp, status, xhr) {
                collection[options.add ? 'add' : 'reset'](collection.parse(resp, xhr), options);
                if (success) success(collection, resp);
            };
            options.error = wrapError(options.error, collection, options);
            return (this.sync || Backbone.sync).call(this, 'read', this, options);
        },

        // Create a new instance of a model in this collection. After the model
        // has been created on the server, it will be added to the collection.
        // Returns the model, or 'false' if validation on a new model fails.
        create: function (model, options) {
            var coll = this;
            options || (options = {});
            model = this._prepareModel(model, options);
            if (!model) return false;
            var success = options.success;
            options.success = function (nextModel, resp, xhr) {
                coll.add(nextModel, options);
                if (success) success(nextModel, resp, xhr);
            };
            model.save(null, options);
            return model;
        },

        // **parse** converts a response into a list of models to be added to the
        // collection. The default implementation is just to pass it through.
        parse: function (resp, xhr) {
            return resp;
        },

        // Proxy to _'s chain. Can't be proxied the same way the rest of the
        // underscore methods are proxied because it relies on the underscore
        // constructor.
        chain: function () {
            return _(this.models).chain();
        },

        // Reset all internal state. Called when the collection is reset.
        _reset: function (options) {
            this.length = 0;
            this.models = [];
            this._byId = {};
            this._byCid = {};
        },

        // Prepare a model to be added to this collection
        _prepareModel: function (model, options) {
            if (!(model instanceof Backbone.Model)) {
                var attrs = model;
                model = new this.model(attrs, { collection: this });
                if (model.validate && !model._performValidation(model.attributes, options)) model = false;
            } else if (!model.collection) {
                model.collection = this;
            }
            return model;
        },

        // Internal implementation of adding a single model to the set, updating
        // hash indexes for `id` and `cid` lookups.
        // Returns the model, or 'false' if validation on a new model fails.
        _add: function (model, options) {
            options || (options = {});
            model = this._prepareModel(model, options);
            if (!model) return false;
            var already = this.getByCid(model);
            if (already) throw new Error(["Can't add the same model to a set twice", already.id]);
            this._byId[model.id] = model;
            this._byCid[model.cid] = model;
            var index = options.at != null ? options.at :
                  this.comparator ? this.sortedIndex(model, this.comparator) :
                  this.length;
            this.models.splice(index, 0, model);
            model.bind('all', this._onModelEvent);
            this.length++;
            options.index = index;
            if (!options.silent) model.trigger('add', model, this, options);
            return model;
        },

        // Internal implementation of removing a single model from the set, updating
        // hash indexes for `id` and `cid` lookups.
        _remove: function (model, options) {
            options || (options = {});
            model = this.getByCid(model) || this.get(model);
            if (!model) return null;
            delete this._byId[model.id];
            delete this._byCid[model.cid];
            var index = this.indexOf(model);
            this.models.splice(index, 1);
            this.length--;
            options.index = index;
            if (!options.silent) model.trigger('remove', model, this, options);
            this._removeReference(model);
            return model;
        },

        // Internal method to remove a model's ties to a collection.
        _removeReference: function (model) {
            if (this == model.collection) {
                delete model.collection;
            }
            model.unbind('all', this._onModelEvent);
        },

        // Internal method called every time a model in the set fires an event.
        // Sets need to update their indexes when models change ids. All other
        // events simply proxy through. "add" and "remove" events that originate
        // in other collections are ignored.
        _onModelEvent: function (ev, model, collection, options) {
            if ((ev == 'add' || ev == 'remove') && collection != this) return;
            if (ev == 'destroy') {
                this._remove(model, options);
            }
            if (model && ev === 'change:' + model.idAttribute) {
                delete this._byId[model.previous(model.idAttribute)];
                this._byId[model.id] = model;
            }
            this.trigger.apply(this, arguments);
        }

    });

    // Underscore methods that we want to implement on the Collection.
    var methods = ['forEach', 'each', 'map', 'reduce', 'reduceRight', 'find', 'detect',
    'filter', 'select', 'reject', 'every', 'all', 'some', 'any', 'include',
    'contains', 'invoke', 'max', 'min', 'sortBy', 'sortedIndex', 'toArray', 'size',
    'first', 'rest', 'last', 'without', 'indexOf', 'lastIndexOf', 'isEmpty', 'groupBy'];

    // Mix in each Underscore method as a proxy to `Collection#models`.
    _.each(methods, function (method) {
        Backbone.Collection.prototype[method] = function () {
            return _[method].apply(_, [this.models].concat(_.toArray(arguments)));
        };
    });

    // Backbone.Router
    // -------------------

    // Routers map faux-URLs to actions, and fire events when routes are
    // matched. Creating a new one sets its `routes` hash, if not set statically.
    Backbone.Router = function (options) {
        options || (options = {});
        if (options.routes) this.routes = options.routes;
        this._bindRoutes();
        this.initialize.apply(this, arguments);
    };

    // Cached regular expressions for matching named param parts and splatted
    // parts of route strings.
    var namedParam = /:([\w\d]+)/g;
    var splatParam = /\*([\w\d]+)/g;
    var escapeRegExp = /[-[\]{}()+?.,\\^$|#\s]/g;

    // Set up all inheritable **Backbone.Router** properties and methods.
    _.extend(Backbone.Router.prototype, Backbone.Events, {

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function () { },

        // Manually bind a single named route to a callback. For example:
        //
        //     this.route('search/:query/p:num', 'search', function(query, num) {
        //       ...
        //     });
        //
        route: function (route, name, callback) {
            Backbone.history || (Backbone.history = new Backbone.History);
            if (!_.isRegExp(route)) route = this._routeToRegExp(route);
            Backbone.history.route(route, _.bind(function (fragment) {
                var args = this._extractParameters(route, fragment);
                callback && callback.apply(this, args);
                this.trigger.apply(this, ['route:' + name].concat(args));
            }, this));
        },

        // Simple proxy to `Backbone.history` to save a fragment into the history.
        navigate: function (fragment, triggerRoute) {
            Backbone.history.navigate(fragment, triggerRoute);
        },

        // Bind all defined routes to `Backbone.history`. We have to reverse the
        // order of the routes here to support behavior where the most general
        // routes can be defined at the bottom of the route map.
        _bindRoutes: function () {
            if (!this.routes) return;
            var routes = [];
            for (var route in this.routes) {
                routes.unshift([route, this.routes[route]]);
            }
            for (var i = 0, l = routes.length; i < l; i++) {
                this.route(routes[i][0], routes[i][1], this[routes[i][1]]);
            }
        },

        // Convert a route string into a regular expression, suitable for matching
        // against the current location hash.
        _routeToRegExp: function (route) {
            route = route.replace(escapeRegExp, "\\$&")
                   .replace(namedParam, "([^\/]*)")
                   .replace(splatParam, "(.*?)");
            return new RegExp('^' + route + '$');
        },

        // Given a route, and a URL fragment that it matches, return the array of
        // extracted parameters.
        _extractParameters: function (route, fragment) {
            return route.exec(fragment).slice(1);
        }

    });

    // Backbone.History
    // ----------------

    // Handles cross-browser history management, based on URL fragments. If the
    // browser does not support `onhashchange`, falls back to polling.
    Backbone.History = function () {
        this.handlers = [];
        _.bindAll(this, 'checkUrl');
    };

    // Cached regex for cleaning hashes.
    var hashStrip = /^#*/;

    // Cached regex for detecting MSIE.
    var isExplorer = /msie [\w.]+/;

    // Has the history handling already been started?
    var historyStarted = false;

    // Set up all inheritable **Backbone.History** properties and methods.
    _.extend(Backbone.History.prototype, {

        // The default interval to poll for hash changes, if necessary, is
        // twenty times a second.
        interval: 50,

        // Get the cross-browser normalized URL fragment, either from the URL,
        // the hash, or the override.
        getFragment: function (fragment, forcePushState) {
            if (fragment == null) {
                if (this._hasPushState || forcePushState) {
                    fragment = window.location.pathname;
                    var search = window.location.search;
                    if (search) fragment += search;
                } else {
                    fragment = window.location.hash;
                }
            }
            fragment = decodeURIComponent(fragment.replace(hashStrip, ''));
            if (!fragment.indexOf(this.options.root)) fragment = fragment.substr(this.options.root.length);
            return fragment;
        },

        // Start the hash change handling, returning `true` if the current URL matches
        // an existing route, and `false` otherwise.
        start: function (options) {

            // Figure out the initial configuration. Do we need an iframe?
            // Is pushState desired ... is it available?
            if (historyStarted) throw new Error("Backbone.history has already been started");
            this.options = _.extend({}, { root: '/' }, this.options, options);
            this._wantsPushState = !!this.options.pushState;
            this._hasPushState = !!(this.options.pushState && window.history && window.history.pushState);
            var fragment = this.getFragment();
            var docMode = document.documentMode;
            var oldIE = (isExplorer.exec(navigator.userAgent.toLowerCase()) && (!docMode || docMode <= 7));
            if (oldIE) {
                this.iframe = $('<iframe src="javascript:0" tabindex="-1" />').hide().appendTo('body')[0].contentWindow;
                this.navigate(fragment);
            }

            // Depending on whether we're using pushState or hashes, and whether
            // 'onhashchange' is supported, determine how we check the URL state.
            if (this._hasPushState) {
                $(window).bind('popstate', this.checkUrl);
            } else if ('onhashchange' in window && !oldIE) {
                $(window).bind('hashchange', this.checkUrl);
            } else {
                setInterval(this.checkUrl, this.interval);
            }

            // Determine if we need to change the base url, for a pushState link
            // opened by a non-pushState browser.
            this.fragment = fragment;
            historyStarted = true;
            var loc = window.location;
            var atRoot = loc.pathname == this.options.root;
            if (this._wantsPushState && !this._hasPushState && !atRoot) {
                this.fragment = this.getFragment(null, true);
                window.location.replace(this.options.root + '#' + this.fragment);
                // Return immediately as browser will do redirect to new url
                return true;
            } else if (this._wantsPushState && this._hasPushState && atRoot && loc.hash) {
                this.fragment = loc.hash.replace(hashStrip, '');
                window.history.replaceState({}, document.title, loc.protocol + '//' + loc.host + this.options.root + this.fragment);
            }

            if (!this.options.silent) {
                return this.loadUrl();
            }
        },

        // Add a route to be tested when the fragment changes. Routes added later may
        // override previous routes.
        route: function (route, callback) {
            this.handlers.unshift({ route: route, callback: callback });
        },

        // Checks the current URL to see if it has changed, and if it has,
        // calls `loadUrl`, normalizing across the hidden iframe.
        checkUrl: function (e) {
            var current = this.getFragment();
            if (current == this.fragment && this.iframe) current = this.getFragment(this.iframe.location.hash);
            if (current == this.fragment || current == decodeURIComponent(this.fragment)) return false;
            if (this.iframe) this.navigate(current);
            this.loadUrl() || this.loadUrl(window.location.hash);
        },

        // Attempt to load the current URL fragment. If a route succeeds with a
        // match, returns `true`. If no defined routes matches the fragment,
        // returns `false`.
        loadUrl: function (fragmentOverride) {
            var fragment = this.fragment = this.getFragment(fragmentOverride);
            var matched = _.any(this.handlers, function (handler) {
                if (handler.route.test(fragment)) {
                    handler.callback(fragment);
                    return true;
                }
            });
            return matched;
        },

        // Save a fragment into the hash history. You are responsible for properly
        // URL-encoding the fragment in advance. This does not trigger
        // a `hashchange` event.
        navigate: function (fragment, triggerRoute) {
            var frag = (fragment || '').replace(hashStrip, '');
            if (this.fragment == frag || this.fragment == decodeURIComponent(frag)) return;
            if (this._hasPushState) {
                var loc = window.location;
                if (frag.indexOf(this.options.root) != 0) frag = this.options.root + frag;
                this.fragment = frag;
                window.history.pushState({}, document.title, loc.protocol + '//' + loc.host + frag);
            } else {
                window.location.hash = this.fragment = frag;
                if (this.iframe && (frag != this.getFragment(this.iframe.location.hash))) {
                    this.iframe.document.open().close();
                    this.iframe.location.hash = frag;
                }
            }
            if (triggerRoute) this.loadUrl(fragment);
        }

    });

    // Backbone.View
    // -------------

    // Creating a Backbone.View creates its initial element outside of the DOM,
    // if an existing element is not provided...
    Backbone.View = function (options) {
        this.cid = _.uniqueId('view');
        this._configure(options || {});
        this._ensureElement();
        this.delegateEvents();
        this.initialize.apply(this, arguments);
    };

    // Element lookup, scoped to DOM elements within the current view.
    // This should be prefered to global lookups, if you're dealing with
    // a specific view.
    var selectorDelegate = function (selector) {
        return $(selector, this.el);
    };

    // Cached regex to split keys for `delegate`.
    var eventSplitter = /^(\S+)\s*(.*)$/;

    // List of view options to be merged as properties.
    var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName'];

    // Set up all inheritable **Backbone.View** properties and methods.
    _.extend(Backbone.View.prototype, Backbone.Events, {

        // The default `tagName` of a View's element is `"div"`.
        tagName: 'div',

        // Attach the `selectorDelegate` function as the `$` property.
        $: selectorDelegate,

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function () { },

        // **render** is the core function that your view should override, in order
        // to populate its element (`this.el`), with the appropriate HTML. The
        // convention is for **render** to always return `this`.
        render: function () {
            return this;
        },

        // Remove this view from the DOM. Note that the view isn't present in the
        // DOM by default, so calling this method may be a no-op.
        remove: function () {
            $(this.el).remove();
            return this;
        },

        // For small amounts of DOM Elements, where a full-blown template isn't
        // needed, use **make** to manufacture elements, one at a time.
        //
        //     var el = this.make('li', {'class': 'row'}, this.model.escape('title'));
        //
        make: function (tagName, attributes, content) {
            var el = document.createElement(tagName);
            if (attributes) $(el).attr(attributes);
            if (content) $(el).html(content);
            return el;
        },

        // Set callbacks, where `this.events` is a hash of
        //
        // *{"event selector": "callback"}*
        //
        //     {
        //       'mousedown .title':  'edit',
        //       'click .button':     'save'
        //     }
        //
        // pairs. Callbacks will be bound to the view, with `this` set properly.
        // Uses event delegation for efficiency.
        // Omitting the selector binds the event to `this.el`.
        // This only works for delegate-able events: not `focus`, `blur`, and
        // not `change`, `submit`, and `reset` in Internet Explorer.
        delegateEvents: function (events) {
            if (!(events || (events = this.events))) return;
            if (_.isFunction(events)) events = events.call(this);
            this.undelegateEvents();
            for (var key in events) {
                var method = this[events[key]];
                if (!method) throw new Error('Event "' + events[key] + '" does not exist');
                var match = key.match(eventSplitter);
                var eventName = match[1], selector = match[2];
                method = _.bind(method, this);
                eventName += '.delegateEvents' + this.cid;
                if (selector === '') {
                    $(this.el).bind(eventName, method);
                } else {
                    $(this.el).delegate(selector, eventName, method);
                }
            }
        },

        // Clears all callbacks previously bound to the view with `delegateEvents`.
        undelegateEvents: function () {
            $(this.el).unbind('.delegateEvents' + this.cid);
        },

        // Performs the initial configuration of a View with a set of options.
        // Keys with special meaning *(model, collection, id, className)*, are
        // attached directly to the view.
        _configure: function (options) {
            if (this.options) options = _.extend({}, this.options, options);
            for (var i = 0, l = viewOptions.length; i < l; i++) {
                var attr = viewOptions[i];
                if (options[attr]) this[attr] = options[attr];
            }
            this.options = options;
        },

        // Ensure that the View has a DOM element to render into.
        // If `this.el` is a string, pass it through `$()`, take the first
        // matching element, and re-assign it to `el`. Otherwise, create
        // an element from the `id`, `className` and `tagName` properties.
        _ensureElement: function () {
            if (!this.el) {
                var attrs = this.attributes || {};
                if (this.id) attrs.id = this.id;
                if (this.className) attrs['class'] = this.className;
                this.el = this.make(this.tagName, attrs);
            } else if (_.isString(this.el)) {
                this.el = $(this.el).get(0);
            }
        }

    });

    // The self-propagating extend function that Backbone classes use.
    var extend = function (protoProps, classProps) {
        var child = inherits(this, protoProps, classProps);
        child.extend = this.extend;
        return child;
    };

    // Set up inheritance for the model, collection, and view.
    Backbone.Model.extend = Backbone.Collection.extend =
    Backbone.Router.extend = Backbone.View.extend = extend;

    // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
    var methodMap = {
        'create': 'POST',
        'update': 'PUT',
        'delete': 'DELETE',
        'read': 'GET'
    };

    // Backbone.sync
    // -------------

    // Override this function to change the manner in which Backbone persists
    // models to the server. You will be passed the type of request, and the
    // model in question. By default, makes a RESTful Ajax request
    // to the model's `url()`. Some possible customizations could be:
    //
    // * Use `setTimeout` to batch rapid-fire updates into a single request.
    // * Send up the models as XML instead of JSON.
    // * Persist models via WebSockets instead of Ajax.
    //
    // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
    // as `POST`, with a `_method` parameter containing the true HTTP method,
    // as well as all requests with the body as `application/x-www-form-urlencoded` instead of
    // `application/json` with the model in a param named `model`.
    // Useful when interfacing with server-side languages like **PHP** that make
    // it difficult to read the body of `PUT` requests.
    Backbone.sync = function (method, model, options) {
        var type = methodMap[method];

        // Default JSON-request options.
        var params = { type: type, dataType: 'json' };

        // Ensure that we have a URL.
        if (!options.url) {
            params.url = getUrl(model) || urlError();
        }

        // Ensure that we have the appropriate request data.
        if (!options.data && model && (method == 'create' || method == 'update')) {
            params.contentType = 'application/json';
            params.data = JSON.stringify(model.toJSON());
        }

        // For older servers, emulate JSON by encoding the request into an HTML-form.
        if (Backbone.emulateJSON) {
            params.contentType = 'application/x-www-form-urlencoded';
            params.data = params.data ? { model: params.data} : {};
        }

        // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
        // And an `X-HTTP-Method-Override` header.
        if (Backbone.emulateHTTP) {
            if (type === 'PUT' || type === 'DELETE') {
                if (Backbone.emulateJSON) params.data._method = type;
                params.type = 'POST';
                params.beforeSend = function (xhr) {
                    xhr.setRequestHeader('X-HTTP-Method-Override', type);
                };
            }
        }

        // Don't process data on a non-GET request.
        if (params.type !== 'GET' && !Backbone.emulateJSON) {
            params.processData = false;
        }

        // Make the request, allowing the user to override any Ajax options.
        return $.ajax(_.extend(params, options));
    };

    // Helpers
    // -------

    // Shared empty constructor function to aid in prototype-chain creation.
    var ctor = function () { };

    // Helper function to correctly set up the prototype chain, for subclasses.
    // Similar to `goog.inherits`, but uses a hash of prototype properties and
    // class properties to be extended.
    var inherits = function (parent, protoProps, staticProps) {
        var child;

        // The constructor function for the new subclass is either defined by you
        // (the "constructor" property in your `extend` definition), or defaulted
        // by us to simply call `super()`.
        if (protoProps && protoProps.hasOwnProperty('constructor')) {
            child = protoProps.constructor;
        } else {
            child = function () { return parent.apply(this, arguments); };
        }

        // Inherit class (static) properties from parent.
        _.extend(child, parent);

        // Set the prototype chain to inherit from `parent`, without calling
        // `parent`'s constructor function.
        ctor.prototype = parent.prototype;
        child.prototype = new ctor();

        // Add prototype properties (instance properties) to the subclass,
        // if supplied.
        if (protoProps) _.extend(child.prototype, protoProps);

        // Add static properties to the constructor function, if supplied.
        if (staticProps) _.extend(child, staticProps);

        // Correctly set child's `prototype.constructor`.
        child.prototype.constructor = child;

        // Set a convenience property in case the parent's prototype is needed later.
        child.__super__ = parent.prototype;

        return child;
    };

    // Helper function to get a URL from a Model or Collection as a property
    // or as a function.
    var getUrl = function (object) {
        if (!(object && object.url)) return null;
        return _.isFunction(object.url) ? object.url() : object.url;
    };

    // Throw an error when a URL is needed, and none is supplied.
    var urlError = function () {
        throw new Error('A "url" property or function must be specified');
    };

    // Wrap an optional error callback with a fallback error event.
    var wrapError = function (onError, originalModel, options) {
        return function (model, resp) {
            var resp = model === originalModel ? resp : model;
            if (onError) {
                onError(model, resp, options);
            } else {
                model.trigger('error', model, resp, options);
            }
        };
    };

    return Backbone;
}));
